Specifications for materials under permeable pavement surface

Summary of specifications for materials under the pavement surface.¹
Link to this table

Material	Specification	Notes
Bedding/choker layer	Pervious concrete: None Porous asphalt: 1inch of AASHTO No. 57 stone PICP: 2 inches of AASHTO No. 8 stone (MnDOT 3127FA-3)	Washed free of fines
Reservoir Layer	Pervious concrete: AASHTO No. 57 stone or per hydraulic design Porous asphalt:AASHTO No. 2, 3, or 5 stone PICP: 4 inches of AASHTO No. 57 base and AASHTO No.2, 3 or 4 stone subbase	Stone layer thickness based on the pavement structural and hydraulic requirements. Stonewashed and free of fines. Recommended minimum void ratio = 0.4.
Underdrain (optional)	Use 4 to 6 inch diameter perforated PVC (AASHTO M-252) pipe or corrugated polyethylene pipe. Perforated pipe installed for the full length of the permeable pavement cell, and non-perforated pipe, as needed,connected to storm drainage system.
Filter Layer (optional)	Sand filter layeris separated from base above and native soils with geotextile. Sand layer typically ASTM C33 gradation, 6 to 12 inches thick.	The sand layer may require a choker layer on surface to provide transition to base layerstone.
Geotextile(optional)	Comply with AASHTO M-288 Standard Specification for Geotextile Specification for Highway Applications, drainage and separation applications, Class I or II. Porous asphalt industry recommends non-woven geotextile.
Impermeable Liner	Use a minimum 30mil PVC liner covered by 12 ounce/square yard non-woven geotextile. EPDM and HDPE liner material is also acceptable.
Observation Well	Use a perforated 4 to 6 inch vertical PVC pipe (AASHTO M-252) with a lockable cap, installedflush with the surface (or under pavers).

¹for additional information on materials referenced in this table (e.g. stone dimensions), see the following links:

• stone size 1, 2 (see Table 1)
• definitions of aggregates 1
• information on geotextiles 1, 2
• liners 1